CN109641315B - Multi-zone focusing lens and laser processing system for wafer dicing or cutting - Google Patents

Abstract

The present invention provides a multi-segment focusing lens for a laser processing method of cutting/scribing/cleaving/cutting, i.e. separating a hard wafer or glass plate of a thick and brittle material, which may be a single plate or have microelectronic or micro-electromechanical devices thereon. The multi-zone focusing lens is used in a laser processing method that includes the steps of modulating a pulsed laser beam, including using shaping and focusing elements with multi-zone lenses; the multi-zone lens generates a plurality of beam convergence zones, more specifically, a plurality of focal points, the intensity distribution of the interference sharp peak-shaped focal points is higher than the optical damage threshold of the workpiece material; the interference sharp peak-shaped intensity distribution is positioned in the workpiece. A changed region is generated in the foregoing step. The laser machining method further includes generating a plurality of the destructive structures at a predetermined fracture line or in a curved track by relatively translating the workpiece with respect to the focal point of the laser beam.

Description

Multi-zone focusing lens and laser processing system for wafer dicing or cutting

Technical Field

The multi-segment focusing lens of the present invention relates to material processing using laser, and more particularly to a method for splitting or cutting hard and brittle materials, various glasses or ceramics by a specially shaped laser beam; the present invention is effective for separating semiconductor devices formed on a substrate.

Background

With the miniaturization and complexity of semiconductor devices, wafer dicing becomes increasingly important in the fabrication of such devices. When the thickness of the silicon wafer exceeds 100 μm, the silicon wafer is conventionally cut with a diamond saw blade, and the silicon wafer with the thickness below 100 μm is cut by a Laser ablation method (Laser ablation).

However, diamond blade technology has the limitation of slow processing speed (for hard materials), and diamond blades also generally produce poor edge cutting quality, such as wider and broken kerf, which reduces the yield and lifetime of the device. This technique is not only expensive due to the rapid wear of the diamond sheet, but is also impractical due to the need to cool and clean the wafer, and the application of this technique to thinner substrates is also limited.

Laser ablation, another conventional processing technique, also has the disadvantages of slow processing speed and a kerf width as high as 10-20 μm, and is not suitable for most applications. However, laser ablation causes cracking and leaves molten debris contaminating the cut area, and this wider heat affected zone reduces the lifetime and performance of the semiconductor device.

Neither laser ablation nor diamond saw blade technology can be applied to specialty wafers with other surface characteristics, such as those with dye-attached films for stack-bonding, and these additional conditions make conventional diamond saw blades and laser ablation methods less suitable and more prone to chipping. In order to improve the quality of the separated devices, other methods and devices based on laser processing have been developed.

US patent 6992026, published on 31.2006, proposes a laser machining method and apparatus which do not produce melting marks when cutting a workpiece, nor do they produce cracks on the surface of the workpiece which extend perpendicularly away from the cutting line. Irradiating the surface of the workpiece with a pulsed laser beam along the predetermined scribe line under conditions sufficient to produce multiphoton absorption, the alignment of the multiple beams producing a focal point (or convergence point, a region of high energy/photon density) on the body of the workpiece, and subsequently moving the focal point along the predetermined scribe line at the cleavage plane, thereby forming a modified area. After the modified regions are generated, the workpiece can be mechanically separated by a small force.

The above-described processing method and its extension technology are now called "stealth dicing", and all of its derivative technologies are based on the generation of internal through holes by focused laser pulse beams. The vias are formed by focusing a pulsed laser beam of a wavelength onto a transparent wafer which, although transparent, absorbs the energy at the focus by a nonlinear process, such as internal etching of a decorative glass block. The internal via, while leaving the top and bottom surfaces intact, typically leaves the wafer in a wafer tape that is mechanically stretched causing the via to break. In contrast, the present invention will not suffer from residue, surface layer cracking, or thermal damage as in the prior art, and can be used to separate custom and multi-layer wafers and MEMS devices.

The disadvantage of stealth dicing is often exacerbated by the necessity of using high numerical aperture lenses that produce low depth of focus (DOF) and tight focus, which can lead to the problem that wafers cleaved in this way can develop multiple cracks at the cleaved surface in varying directions that can affect the lifetime of the devices thereon. Meanwhile, the stealth dicing is also not favorable for sapphire processing, and when processing wafers and substrates with thickness less than 120-140 μm, the defect of the technique is not obvious because only one time is needed to pass through each separation line to be diced; however, when processing thicker wafers (typically 4 inch, 6 inch sapphire wafers having a thickness of 140 μm to 250 μm or more), each separation line needs to pass several times, which increases the time that the material is exposed to laser radiation, thereby negatively affecting the performance of the final device. In addition, the processing flow that each separation line needs to pass through many times also slows down whole processing speed and output.

US patent US2013126573, published 5/23/2013, proposes another material processing method, which is a pre-flow of the cleaving step, for the internal processing of transparent substrates. Irradiating the focused laser beam onto the substrate by selecting a pulse energy and a pulse duration of the pulse to generate a filament inside the substrate; translating the irradiated substrate relative to the laser beam to create additional filaments at additional locations; the resulting filaments will form an array that will define the internal scribe path for cleaving the substrate. The length and position of the filament can be varied by adjusting the laser beam parameters, or alternatively, a V-shaped groove that produces a laser cleaved edge bevel can be used. Preferably, the laser pulses are delivered in pulse trains to reduce the energy threshold for filament formation, increase filament length, anneal filament formation zones to minimize additional damage. Therefore, the method can improve the processing reproducibility and processing speed relative to the use of a low pulse repetition rate laser.

However, this method results in uneven processing results and is therefore only suitable for bare materials, and cutting is inconvenient because of the high pulse energy required. Higher pulse energies can also have a negative impact on the performance of the resulting semiconductor device, especially when the wafer is diced using LEDs with increased leakage current, such as High Brightness (HB) and Ultra High Brightness (UHB) LEDs, which can severely degrade the performance of the semiconductor device.

US2009032511, published 2/5/2009, proposes a laser beam manipulation method for material processing by laser, and more specifically, a method for improving beam shaping and beam homogenization. The invention relates generally to an optical system that is capable of stably delivering a consistent amount of energy to the entire annealing region of a substrate surface; the optical system is used to deliver or project a uniform energy having a desired two-dimensional shape, typically a square or rectangle, to a target area on the substrate surface. In general, the optical systems and methods of the present invention preferentially anneal one or more of the plurality of anneal zones by delivering energy sufficient to cause remelting and solidification of one or more of the zones.

Another german patent DE102004001949, published at 11/8/2005, proposes a laser processing system that uses a multi-zone lens to focus the output laser light into a parallel axis, which can also be used for material processing with laser light. Utilizing five lens sections surrounding a circular lens surface at equal intervals, the focal points of the lens sections pointing to a fiber duct; directing a laser beam toward the lens; thus, the laser can be optimally focused at an output point corresponding to the surface of the workpiece.

US2013256286 published in 2013, 10/3, proposes a laser processing method using a light-scattering elongated beam spot and an ultra-short pulse, which uses an adjustable elongated beam spot formed by a laser beam having an ultra-short laser pulse and/or a longer wavelength to process substrates made of different materials. The laser beam may be generated by pulses having a pulse duration of less than 1ns and/or a wavelength of greater than 400 nm. When the laser beam is modulated, an astigmatic beam is produced which is collimated on a first optical axis and converged on a second optical axis; focusing the astigmatic beam on the substrate to form an elongated beam spot by focusing on a first optical axis and defocusing on a second optical axis on the substrate; the length of the elongated beam spot is adjusted to an energy intensity sufficient to provide a single ultrashort pulse to produce cold ablation of at least a portion of the substrate material.

US2012234807, published on 9/20/2012, proposes a laser scribing process that can extend into the depth of the workpiece. The method is based on focusing the laser beam to induce a deliberate aberration, adjusting the range of longitudinal spherical aberration to a depth sufficient to extend the focus into the workpiece by limiting the range of transverse spherical aberration. The method can also cause uneven processing results because the high-energy pulse generates a vertical damage track in the workpiece; high pulse energies are necessary because this method necessitates the use of low numerical aperture lenses (focal lengths of tens of millimetres), but the use of such lenses results in a loose focusing situation, i.e. the spot has a very smooth spatial intensity profile, thus causing operating conditions exceeding the damage threshold flux in large areas with relatively low peak values. Increasing the pulse energy with increasing pulse intensity requirements (needed for optical melting) also makes the processing of High Brightness (HB) and Ultra High Brightness (UHB) LEDs less attractive at the LED leakage current, and the chip edge roughness and cracking are as severe as in the previous methods.

International patent WO2016059449, published in 2016 and 21.4.2016, proposes a laser processing method for cleaving or cutting a substrate by forming a sharp-peak-shaped breaking structure, which provides a laser processing apparatus and method for rapidly separating semiconductor devices formed on a single substrate or substrates of a high-thickness hard and brittle material. The device or substrate for cleaving or breaking, during the pre-operation, creates a deep and narrow destruction zone along a predetermined cleavage line, resulting in a destruction zone. The laser processing method includes the step of modulating a pulsed laser beam using a focusing element to produce a peaked beam convergence region, and more specifically, a fluence (energy distribution) above the optical damage threshold of the workpiece material, during which a modified region (having a peaked shape) is formed. The laser machining method further includes relatively translating the workpiece with respect to the laser beam convergence point to produce a plurality of the failure structures at a predetermined fracture line.

Patent US2015151380a1 discloses a laser processing method using distributed focusing lenses, a focusing path of the beam of electric radiation and filamentation in the focusing region, which is considered as a coarser processing procedure than interference focusing and multiphoton absorption.

The laser processing method disclosed in patent application CN103551732A employs a multi-focus Diffractive Optical Element (DOE) which is used in tandem with at least one plano-convex focusing lens.

Patent US2005024743a1 discloses an aspherical lens having at least one aspherical surface with a bending force for focusing an incident beam ray to a straight section located on the optical axis of the optical component, but the lens and the method relate to a method of machining opaque materials, such as metals, alloys, using shear marks related to laser ablation methods.

When the prior art is applied to the separation of wafers, it is significantly deficient in terms of substrate thickness, material type, and processing quality. Meanwhile, in order to process a thicker material, the above method must increase the laser intensity, the number of times the laser beam passes through each of the separation lines, and improve the shape of the beam or focus, which consequently affects the performance and yield of the semiconductor device.

Disclosure of Invention

To reduce the above-mentioned disadvantages, the present invention provides a multi-segment focusing lens for an efficient and rapid laser processing method for separating semiconductor or micro-electromechanical devices formed on a single-layer substrate, or for separating a high-thickness hard substrate, glass plate or ceramic plate. The pre-processing of wafers or substrates for cleaving or breaking (dicing) entails the use of laser machining methods, characterized in that the resulting cleaving line has deep and narrow damage zones. The laser processing method of the invention does not need to pass each cutting line by the laser beam for many times, thereby improving the efficiency. The term "workpiece" as used herein includes substrates, wafers, glass sheets, semiconductor devices, or the like that are prepared for processing and then mechanically separated (or alternated).

The laser processing method includes the step of modulating a pulsed laser beam using a focusing element (1). One of the optical surfaces of the focusing element includes a plurality of segments having different radii of curvature. The beam diverges and is adjusted in diameter and focused onto a workpiece body, thereby forming a plurality of focal points in the beam convergence region, more specifically, spaced at a distance on the optical axis of the multi-segmented lens, each of which is above the optical damage threshold flux (energy distribution) of the workpiece material.

The material should be locally or completely transparent to the wavelength of the laser radiation, preferably with a band gap above 0.9 eV. For the irradiation of the workpiece, the array of multiple focal points is within the thickness of the workpiece. The array of multiple focal points forms a peaked structure in which the energy distributions of the multiple focal points overlap to form an interference that is an extension of the high intensity region of the laser radiation. The fluence is set such that multiphoton absorption occurs, thereby causing local melting or coulomb explosion, the absorption occurring at one of the plurality of focal points, or at all interference extending from the high intensity region of the laser radiation. Along the determined cutting track, a continuously changed region (by extending a strip-shaped interference field of the plurality of focuses) is generated in the material body, and the region is a damaged structure.

The laser machining method further comprises relatively translating the workpiece (2) with respect to the laser beam focus, thereby creating a plurality of said destructive structures at a predetermined fracture line. After forming the fracture line, the object can be separated or cut into 2 or more smaller parts by the mechanical force, each part having a separation boundary bounded by a series of fracture zones.

Drawings

For a better understanding of the method and to understand its practical application, reference will now be made to the following drawings, which are provided by way of example only and are not intended to limit the scope of the present invention.

FIG. 1 is a schematic view of a laser beam propagating through a multi-segment lens of the present invention, each line segment representing the boundary of a different portion of the beam, wherein each portion is shaped by a respective segment of the lens surface to produce a different focal point;

FIG. 2 is a schematic view of the light tracing of the present invention, wherein a multi-segment lens is used to focus an incident laser beam with Gaussian intensity distribution to form the light tracing inside a workpiece, and each segment of the beam is focused on the same optical axis inside the material to generate a continuous damage structure to form a splitting/cracking surface;

FIG. 3 is a schematic diagram of a laser processing method and its optical system according to the present invention;

FIG. 4 shows an embodiment of the present invention, in which the beam splitter and the beam shaper are used to separate two arms, and then the two paths are overlapped again and guided to the focusing device;

FIG. 5 is a ray trace geometry of the present invention with multiple focal point (24) positions, which is numerically calculated from the incident laser light passing through the lens (1);

FIG. 6 is a graph showing the intensity distribution of interference of the present invention with a peak (25) of a specific length in the light transmission direction, which is numerically calculated from the incident laser beam passing through the lens (1);

FIG. 7 is a graph of the light intensity distribution (26) of the present invention numerically formed along the peak (25);

FIG. 8 is an electrical representation of a surface crack (18) on the workpiece surface (2) after processing with a high numerical aperture aspheric concentric ring lens (1) focusing two laser beams having different divergences;

FIG. 9 shows laser-induced damage at the fracture edge of a workpiece, which is a lithium niobate wafer having a thickness of about 190 μm; the first laser beam path is 60 μm wide in front of the breaking region (27), and the second laser beam path is 100 μm wide in succession to the breaking region (28); focusing two laser beams having different divergences to an aspherical lens (1) of the multi-focal-point high-numerical-aperture section, the fracture edge crack being the result of the machining of the workpiece in this way.

Detailed Description

The present invention provides a multi-segment focusing lens for laser processing methods and systems for separating semiconductor or microelectromechanical devices formed on a single layer substrate, or for separating rigid substrates. The specimen for cleavage or breakage, which is subjected to a preliminary operation, is subjected to a destruction zone, characterized in that the resulting cleavage line has deep and narrow destruction zones along the cleavage line.

In one embodiment, the processing method comprises the steps of: providing a pulsed laser beam (13); focusing the laser beam (13) with a focusing element (1); irradiating a workpiece (2) with the focused pulse laser beam (13); forming a continuous fracture zone (18) to produce a cleavage plane; the workpiece (2) is made of a material which is transparent to the laser radiation and has an energy gap (band gap) which is higher than a photon energy of the laser beam (13); the focusing of the laser beam (13) by the beam focusing element comprises the use of a multi-segment lens (1), wherein at least one surface of the lens (1) has a plurality of segments of different radii of curvature, each of the surface segments having a different focal length; the different focal lengths of the segments are used to produce spatially separated focal points on an optical axis, more specifically, when a specially pre-shaped laser beam (13) passes through the lens (1), the incident light rays passing through the different curvature regions are focused into focal points (24); the asphericity of each of the plurality of zones ensures that no spherical aberration occurs at the plurality of focal points (24). The dimensions of the regions (3-7) are selected such that the energy of the beam (13) in the shape of a Gaussian between the focal points (24) is evenly distributed. The lens (1) is designed with a high numerical aperture to produce tight multiple focusing; the short distance of the focal points (24) from one another and the energy distribution determine the formation of an interference intensity distribution (26) in the light transmission direction. The distribution may also be considered as a high intensity peak (25) of a particular length.

FIG. 6 shows a numerical calculation of the two-dimensional intensity distribution, the convergence of the multiple focal points (24) into a longer peak (25) greatly increases the depth of extension into the substrate compared to conventional aspheric lenses with a single focal point, which is a key feature of the present invention. FIG. 7 shows a numerically calculated intensity distribution (26), the intensity distribution (26) being along the light transmission direction of the laser beam (13) forming the peak (25). The peak (25) is necessary to induce optical melting loss, i.e. to reach a flux (energy distribution) in the bulk of the workpiece (2) higher than the optical damage threshold; this energy distribution is formed along the thickness of the substrate in the interior of the substrate for splitting a wafer (2) or sheet into smaller parts.

In one embodiment, the aspect ratio of the peaked flux distribution is more than 50 times, i.e., the longitudinal direction is more than 50 times the transverse direction.

Two of the laser beams (13) having different divergences are simultaneously directed through the aspherical lens (1) shown in fig. 1, the lens (1) having a special design of the multi-focal-point high numerical aperture section, fig. 8 and 9 show the result after actually processing with two of the laser beams (13).

FIG. 8 shows a superficial crack (18) on the surface of the workpiece (2) by focusing two of the laser beams (13) having different divergences onto the aspherical lens (1) of the multi-focal-point high-numerical-aperture section, the crack (18) being the result of the machining of the workpiece (2) in this way.

FIG. 9 shows the laser-induced damage region at a fracture edge of a lithium niobate wafer having a thickness of about 190 μm, the path of the first laser beam (13) being the first 60 μm extent of the damage region (27); the path of the second laser beam (13) is such that the destruction zone (28) is in the range of the following 100 μm. This is an example of another preferred embodiment, which uses the single multi-zone lens (1) as described above to focus a number of the multiple beams (13) with different dispersions simultaneously.

The step of irradiating the workpiece (2) with the focused pulse laser beam (13) can simultaneously traverse the workpiece (2) in a direction transverse to the optical axis of the focusing element (1). The beam (13) is focused to form a plurality of beam convergence zones (focal points) within the body of the workpiece (2), the plurality of focal points (24) producing the plurality of destructive structures conforming to or approximating the shape of the convergence zones. By the spatial flux distribution of the convergence region being in the shape of the focal structure shown in FIG. 2, the convergence region will be formed where the flux is above the material damage threshold of the workpiece (2).

The term "failure" in the present invention refers to any type of change in the material produced locally sufficient to cause a change in the mechanical properties of the material sufficient to produce a controlled crack (18) (along the separation boundary) in a subsequent cleaving step; the altered or destroyed structure (locally destroyed region) is induced by the mechanism of multiphoton absorption. If the material of the workpiece (2) is partially or completely transparent to the central wavelength of the laser radiation used (the energy gap of the material is higher than the energy of a single photon, preferably several times higher), and a sufficient photon density is reached, the destructive structure is produced; sufficient photon density is achieved using short and very short pulses and is condensed closely in space, for example, by focusing of the light beam (13). The energy gap of the material of the workpiece (2) is preferably higher than 0.9 eV.

The method further comprises repeatedly irradiating the sample at spaced locations of the line of disruption or separation formed by the plurality of disruption structures (18) by mounting the workpiece (2) to a motorized linear translation stage assembly (17) and moving the workpiece (2) in a desired direction along the line of disruption defined thereby to form a cleavage plane. However, the translation stage (16) may also use different combinations of motorization of the focusing unit, including rotary stages, gantry stages, as long as the relative movement of the focusing unit and the workpiece (2) is ensured. Any wafer-shaped substrate can be used as the workpiece (2) of the present invention if it is hard and brittle, has an energy gap of 0.9eV or more, and is difficult to machine.

In another embodiment, the positioning system translates the workpiece (2) (or the focusing element) in a curved, circular or elliptical path, i.e., a free-form path, thereby cutting a plurality of two-dimensional structures from a sheet, particularly for processing amorphous or polycrystalline materials, such as glass or ceramic, including chemically strengthened glass.

In one embodiment, the processing step is accomplished with a pulsed laser beam (13) source (14) for generating a beam (13), preferably a Gaussian intensity distribution (26) of circular-elliptical shape; a beam shaping and focusing unit (1,15,16) comprising a combination of a beam focusing element (1) and a beam shaping unit (15); means for stabilizing the distance between the beam focusing element (1) and the workpiece (2) as shown in FIG. 3; means for holding and translating a workpiece (2), such as a motorized translation stage assembly (17). The pulsed laser beam source (14) is preferably capable of producing the laser pulses in a constant polarization for a steady duration, with a well-defined temporal envelope of the laser. Preferably a Gaussian pulse having a pulse duration set at 100-15000fs, a central wavelength set at 500-2000nm, a frequency set at 10kHz-2MHz and a pulse energy sufficient for the pulses after passing through the shaping and focusing unit (1,15,16) to still have a pulse energy in the range of 1-100 muJ. A beam shaping optical lens (15), preferably comprising a beam expander (15), such as a beam expander (15) of the type of a Crabler telescope or a Galilean telescope, or any combination thereof, which achieves an appropriate beam width and divergence before the beam (13) enters the focusing element (1). The beam focusing unit (1), preferably comprising a multi-segmented lens (1), and means for maintaining a predetermined distance between the lens (1) and the workpiece (2), for example, a distance monitoring device with a piezo-nano positioner or motorized linear translation stage (16), maintains the distance between the beam focusing unit (1,15,16) and the workpiece (2) within the working distance of the focusing element (16) and with an error of no more than about 2 μm when translated at a speed of 300 m/s. The beam focusing element (1) is arranged so as to be able to achieve a focal shape (spatial distribution of flux above the damage threshold of the workpiece (2)) equal to the spatially high intensity distribution (26) of the multifocal shape shown in figure 2, when the beam (13) is focused on a plurality of places of the workpiece (2). The resulting destructive structures (18) may also extend from a first surface (19) of the workpiece (2) to the interior of its body, if desired, for example to induce an ablation (the ablation that produces a pit (20)) at the surface (19).

A numerical aperture of the beam focusing element (1) is preferably high (numerical aperture >0.7), but in other embodiments the numerical aperture may be selected in the range of 0.5-0.9, as long as the lens (1) is designed to form the plurality of different sections with different radii of curvature in the lens (1), which sections may produce a plurality of focal points (24), preferably one such section for producing one such focal point. FIG. 2 shows a ray trace of a convergence zone.

But in one instanceFor example, the beam focusing element (1) may be the multi-zone lens (1) (see fig. 1), the lens (1) being arranged to form a multi-focal spot of the beam (13). A concave surface of the lens (1) has more than 2 of the plurality of sections, which have different radii of curvature and are characterized by the plurality of different focal points. The plurality of segments are smoothly varied between them such that the plurality of spots are gradually switched to form a peaked focus having a plurality of higher flux regions. The incident laser beam (13) is preferably expanded such that the cross-sectional area of the beam (13) covers more than 90% of the aperture of the lens (1), the lens (1) being capable of adding multiple focal points (24) (see fig. 2); in this preferred embodiment, the light beam (13) should be adapted to the lens (1) such that the Gaussian beam (13) has an intensity of 1/e as it approaches the clear aperture (clear aperture) circumference of the multi-segment lens (1)²To a certain extent.

Preferably, the spacing between the laser pulses delivered to the surface is in the range of 0.1 μm to 10 μm, and the range of distances can be varied by varying the speed of movement of the motorized translation stage assembly (17) or the laser pulse repetition rate, or both. The cleavage/break line (18) is formed by linearly moving the motorized translation stage assembly (17) up to 2 passes (repeated translations), but not limited to 2 passes, for a single cleavage line. In this case, the compactness of the focus is related to the formation of multiple focal points, which can be controlled by the parameters of the multi-segment lens (1), the optical properties of the material of the lens (1), or the properties of the incident light beam (13).

An objective lens of the lens (1) is designed in accordance with the plurality of workpiece (2) parameters, such as thickness, energy gap value, absorption, refractive index, etc. The lens (1) is designed such that the Gaussian beam or the flat-top beam has a preferred flux distribution between the plurality of focal points (24) to vary the size or surface area of the plurality of sections of the lens (1).

In another embodiment, the same beam focusing element (1) is used to simultaneously focus four of the multiple laser beams (13) having different divergences, thereby creating multiple arrays of the multiple focal points (24), thereby increasing processing speed or allowing the processing system to be used to process thicker wafers.

One embodiment of the aforementioned embodiment is an optical system having means for splitting the laser beam (13) into a plurality of beam combinations, for example the plurality of elements with different polarizations (polarization), or by delaying the temporal or spatial separation of the plurality of elements. The laser beam (13) can be split into multiple groups by birefringent means (beam splitters, polarizers, prisms, or other optical elements), and the aforementioned method of varying the convergence of the incident beam (13) can be used to adjust the parameters of the beam (13) at each optical path separately. Thus, a plurality of the laser beams (13) are shaped and focused to form a plurality of the converging regions (i.e., focal points), the plurality of focal points (24) having substantially the same distance from each other, thereby creating a plurality of narrow the damage structures within the material or a more evenly distributed flux, and thus, overall process speed may be increased or a higher precision rate may be achieved. Figure 4 shows one of the possible beam splitter (22) component types, the main difference between the other beam splitters being that they can be replaced by a different beam shaping component. The complete beam shaping element (23) can be placed in each of the optical paths (as shown in fig. 4). In another embodiment, two sets of the divergence control elements (e.g., Galileo telescope) can be separately disposed on each of the optical paths; but before the focusing element (1), the beam shaper (15), e.g. a set of lenses, is arranged in the common optical path. In another embodiment, the two sets of divergence control elements (e.g., Galileo telescope) (23) can be separately disposed in each of the optical paths. But before a first beam splitter (22), the beam shaper (15) (e.g., a set of lenses) is disposed in the common optical path.

In another embodiment, the step of irradiating the workpiece (2) with the focused pulsed laser beam. The beam focusing element is disposed to include at least one diffractive element for expanding or replacing the beam shaping optical group, the diffractive element shaping the incident beam to generate a plurality of the focal points after the beam passes through the beam focusing element (1).

In another embodiment, however, the step of irradiating the workpiece (2) with the focused pulsed laser beam via a beam shaping and focusing element (1,15, 16). The beam shaping element is arranged to comprise at least one adaptive optical element which shapes the incident beam after it has passed through the multi-zone lens (1), producing a multi-focal intensity distribution, thus allowing the use of more different incident beams (or beams of more specific and different modulation) or allowing compensation for variations in processing parameters. The beam shaping element (23) may be based on a deformable mirror, a piezo-deformable mirror, or the like.

In another embodiment, however, the step of irradiating the workpiece with the focused pulsed laser beam is performed. According to the above embodiments, the adaptive optics may be replaced by at least one phase or amplitude modulation element, such as a liquid crystal light modulator or a micro-mirror matrix.

In another embodiment, however, the step of irradiating the workpiece (2) with the focused pulsed laser beam via a beam focusing element (1,15, 16). According to the above embodiments, the adaptive optics may be replaced by at least one passive diffractive beam modulating element, such as a flat top beam shaping diffractive optical element (or diffractive optical elements) for correcting aberration or astigmatism. The passive diffractive element (passive differential element) is selected such that a beam (13) modulated by the elements is focused by the beam focusing element (1) to the multifocal intensity distribution (26). It should be noted that the element may also be arranged in the optical path after the beam focusing element (1).

In another embodiment, the beam focusing element is preferably the multi-segmented lens (1), the focusing element modulating a spot of the beam (13) in the pattern shown in FIG. 2; the segments of the light beam (13) are influenced by the multi-segment lens (1), the light beam (13) striking the surface (19) of the workpiece (2) and being slightly refracted and focused in the following manner: a plane (8) perpendicular to an optical axis of the multi-segment lens (1), the light beam (13) at the plane (8) propagating through the plurality of focal points of the segment (7); wherein (9) is a focal plane of the section (6); (10) is a focal plane of the section (5); (11) is a focal plane of the section (4); (12) is a focal plane of the section (3).

In order to better illustrate the present invention, an example is presented below, which together with the parameters disclosed serve only to facilitate a better understanding of the present invention, without in any way limiting its scope, the parameters may be varied considerably to produce similar or different results, but the main concept of the cropping process is the same.

The workpiece (2) is made of lithium niobate and has a thickness of about 190 μm. The laser light source (14) is a femtosecond laser having an output radiation wavelength of 1030nm and a pulse width of 5ps (full width at half maximum 1.41), and the output frequency is set to 100 kHz. The focusing unit uses an aspherical lens (1) having a numerical aperture of less than 0.8 for the multi-focusing section as the light beam focusing element.

Two laser beams (13) having different divergences are combined and directed through the focusing element (1), the pulse energy after passing through the beam focusing element is selected to be 3 muJ and 5 muJ, respectively, and the convergence regions of the first and the second beams (13) are formed at 20 muM and 80 muM below the first surface of the wafer, respectively. The distance between the destruction structures in the cleaving direction is 3 μm, the processing speed, more specifically the translation speed of the linear translation stage (16) is 300mm/s, and FIG. 9 shows the results after the breaking and cutting process.

Claims (20)

1. A multi-segment focusing lens for use in a laser processing method for substrate cleaving and dicing, comprising: providing a pulse laser beam; focusing the laser beam with the multi-segment focusing lens; irradiating a workpiece with the focused pulse laser beam; and forming a continuous damage region to generate a cleavage plane; wherein the workpiece is made of a material that is transparent to the laser radiation and has an energy gap that is higher than a photon energy of the laser beam;

the multi-zone focusing lens is characterized in that:

it is a single refractive multi-segment lens in which at least one surface of the lens has multiple segments of different radii of curvature, axially symmetric and concentrically aligned with each other, each of the surface segments having a different focal length; wherein the plurality of different focal lengths of the plurality of segments are used to generate a plurality of spatially separated focal points that are an intensity distribution of the interfering peaked focal points.

2. The multi-segment focusing lens for a laser processing method of claim 1, having more than two segments, wherein said plurality of segments have different radii of curvature.

3. The multi-segment focusing lens for a laser processing method of claim 1, wherein the plurality of segments of the multi-segment focusing lens have an aspheric nature, the plurality of segments being arranged to reduce spherical aberration of the plurality of focal points.

4. The multi-segment focusing lens for a laser processing method of claim 1, wherein the multi-segment focusing lens focuses the laser beam by impinging the multi-segment focusing lens with a plurality of transverse beam combinations to focus to a corresponding plurality of focal points along an optical axis of the lens, the plurality of focal points having substantially the same distance from each other.

5. The multi-segment focusing lens for a laser processing method as claimed in claim 1, wherein the dimensions of the plurality of segments are selected so that the energy of a beam having a gaussian energy distribution in cross section is evenly distributed among the plurality of focal points.

6. The multi-segment focusing lens for a laser processing method as claimed in claim 1, wherein the distance and energy distribution of the plurality of focal points from each other determine the formation of the intensity distribution interfering along the light transmission direction to form a peaked flux distribution having a specific length, thereby extending into the depth of the substrate being cleaved or diced.

7. The multi-segment focusing lens for a laser processing method as claimed in claim 6, wherein the aspect ratio of the peaked flux distribution is 50 times or more.

8. The multi-segment focusing lens for laser processing according to claim 1, wherein the workpiece irradiated by the focused pulse laser beam is a wafer-shaped substrate, wherein the substrate is a hard and brittle material or glass with an energy gap higher than 0.9eV, and the hard and brittle material is SiC, GaN, sapphire, diamond, or lithium niobate.

9. A laser processing system for cutting, scribing, dicing or cleaving a wafer, comprising: a pulsed laser light source; a focusing element; and an actuating positioning system for positioning the wafer; the method is characterized in that: the focusing element is the multi-segment focusing element of any one of claims 1 to 8.

10. The laser machining system of claim 9 further comprising a positioning stage associated with the focusing element, the positioning stage configured to maintain the plurality of focal points in a fixed position relative to the plurality of workpiece surfaces.

11. The laser machining system of claim 9 wherein said step of forming a continuous break area includes translating said workpiece relative to said focused laser beam to produce a cut line, and repeating said steps until said workpiece is cut to a desired size.

12. The laser machining system of claim 9, wherein the translation is according to a predetermined trajectory, the trajectory being formed along a plurality of destructive structures spaced apart from each other by 0.1-10 μm, and including a plurality of portions in a straight line, a curved line or a circle.

13. The laser processing system of claim 9, further comprising a beam shaping unit for splitting the incident beam into at least two optical paths and controlling the divergence of each of the optical paths, respectively, the beam shaping unit further combining the beam from the at least two optical paths into a single optical path.

14. The laser machining system of claim 13, wherein the system is configured to split the beam into two to eight separate optical paths.

15. The laser processing system of claim 9 further comprising at least one passive diffractive element, a phase or amplitude modulating element, a birefringent element, a plurality of aberration correcting elements, a top beam shaping diffractive element, or any adaptive optical element.

16. The laser processing system of claim 9, wherein the pulsed laser light source is configured to emit the laser radiation in a wavelength range of 500nm to 2000nm, or a standard laser that is tuned to the wavelength range by parametric optics.

17. The laser processing system of claim 9, wherein the pulsed laser light source is configured to emit laser pulses having a repetition rate in a range of 10kHz to 2MHz and a duration in a range of 100fs to 15000 fs.

18. The laser processing system of claim 9, wherein the pulsed laser light source is configured to emit laser pulses having a pulse energy in a range of 1 μ J to 100 μ J.

19. The multi-segment focusing lens for laser processing according to claim 1, used in a laser processing method and system for separating semiconductor or micro-electromechanical devices formed on a single layer substrate, or for separating a high thickness hard substrate, glass plate or ceramic plate.

20. The multi-segment focusing lens for a laser machining method of claim 1, wherein an intensity distribution of the interference peaked focus is located below the surface of the workpiece.

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